This huge number is illegal under US law

The strange legal quirk has its roots in copyright law and DVD piracy

The number is a representation of an illegal DVD decryption algorithm (Peter Macdiarmid/Getty Images)

All those urban legends about crazy American laws may not be entirely grounded in reality, but one definitely is - there's 1,401-digit number which, according to the 1998 Digital Millenium Copyright Act, is illegal to possess.

This strange revelation comes from YouTuber WendoverProductions, whose latest video sheds some light on this strange legal quirk.

The reason for the number's illegality is all down to copyright law and DVD piracy.

DVDs are often encrypted, as a measure to stop people making copies of them. As DVD adoption grew, software was released which allowed people to get around these security measures.

Film studios noticed this, and brought legal cases - eventually, the software was banned under the DMCA, which made it illegal to circumvent copyright measures, or distribute tools which could.

That's where our number comes in. The huge number, which is a prime, is the binary representation of a compressed version of the source code of the DVD decryption algorithm. As a result, possessing it is just as illegal as owning the copying software.

Naturally, the odds of anyone actually being prosecuted for possessing the number is very low, since filesharing is so widespread and film studios aren't as litigious over digital piracy as they were in the late '90s.

However, the law is still on the books. Next time you visit the US, make sure you don't have the 1,401-digit number written down anywhere, unless you want to get into some trouble at the border.